Combined dipole and linear antenna with balun



Oct. 1, 1968 I J. H. THEAKSTON I 3,404,404

COMBINED DIPOLE AND LINEAR ANTENNA WITH BALUN Filed May 24, 1965 United States Patent 3,404,404 COMBINED DIPOLE AND LINEAR ANTENNA WITH BALUN John Herbert Theakston, Westonia, Weston Favell, England, assignor to J. Beam Aerials Limited, Rothersthorpe Crescent, Northampton, England Filed May 24, 1965, Ser. No. 457,915 4 Claims. (Cl. 343-727) ABSTRACT OF THE DISCLOSURE This invention concerns a transformer or balun for a radio antenna intended for the reception of an optimum frequency or band of frequencies, and employing balanced radiator elements, such as a folded dipole. The transformer comprises a former on which a wire is noninductively wound, the ends of the wire being connected to said elements. The conductors of a feeder cable are connected to the former and to one of said elements respectively.

This invention concerns radio antennae intended for the reception of an optimum frequency or band of frequencies, and employing a balanced radiator element, such as a folded dipole.

It is customary to use a low-impedance feeder cable for connecting the radio apparatus to the antenna, and generally to match the impedance of the cable to the aerial it is desirable to use some transformer means.

It is the main object of the invention to provide an improved transformer arrangement for converting from balance to unbalance, i.e., a balun to effect correct connection of the feeder cable to the antenna without upsetting the balance of the antenna.

Another object is to provide a balun of simple construction which can also support the radiator elements of the antenna. A further object is to provide a balun which enables a further antenna (or antennae) to be connected, and of a construction for reception of a frequency or band of frequencies other than the said optimum.

With the above, and other objects which will be apparent from the following description, in view, reference will now be made to the accompanying drawings illustrating by way of example and in perspective, a preferred construction of transformer or balun arrangement according to the invention.

In the drawing, reference represents one length of a folded dipole, which length is broken in the centre for the connection of the feeder cable. The ends enter an insulating housing 11 and extending from the housing 11 are the heads 12, 12a of two terminal members which connect with the respective ends of the broken length of dipole.

A third terminal 13 is provided, projecting from which is an angle bracket 14 to which is clamped the outer screened conductor (not shown) of a low impedance coaxial feeder cable, and a tubular metal former 15 around which is wound a length of insulated wire 16, opposite ends of which are connected electrically to the terminals 12, 1201. To the terminal 12 is connected the inner conductor (not shown) of the said coaxial feeder. The insulated wire 16 is substantially half a wavelength long at the optimum frequency, the reactive correction factor of the radiator or antenna (.dipole) being dependent on ice the insulation of the wire, and the length of the wire wound on the former. The latter is adjustable.

The connection shown and described gives a balance to unbalance transformer and step down ratio from the radiator input. Similarly, a twin feeder cable can be connected across the two balanced terminals 12, 12a. The insulated wire is noninductively wound, for example, bifilar wound.

A shround 17, shown in broken lines, is provided for the coil 16. This shroud 17 is optional. It can be in the form of a metal clip which has a lug secured by the bracket .14 and terminal 13, and can have an insulating lining.

The metal former may be earthed to the antenna framework.

Furthermore, in a variation, the metal former is connected to an element 18 or elements for picking up frequencies other than the said optimum. These other frequencies will be transferred to the feeder, but as the former is at the electrical balance point of the primary or main antenna 10, they will have no effect upon the performance of that antenna.

Various other modifications may be made to the preferred construction. For example, the former 15 can be of any other suitable electrically conducting material. The metal former, on the other hand, can be surrounded by an insulating lining and the wire 16, which need not be insulating, wound around the insulating lining.

Although the preferred construction has been described in connection with a folded dipole, it is to be understood that the invention can be used with any other type of balanced antenna arrangement.

It will be understood that in practice, a suitable cover such as a snap-on or screw-on cover, will be provided for the housing to cover over the terminals, former and wire, shroud and clamp. This cover is not shown in the drawing.

I claim:

1. A transformer for an antenna for high frequency operation for the reception of an optimum frequency or band of frequencies, comprising an insulating housing, a balanced radiator mounted on said housing, a metal former in said housing, a length of wire having two ends wound noninductively around said former, said length being dependent on a correction factor for the radiator, terminals in said housing for carrying elements of the radiator, the two ends of said wire being connected to said terminals respectively, cable clamping means secured to said housing and adapted to clamp a low impedance feeder cable to said housing, and means for connecting such feeder cable to said former and to one of said terminals.

2. A transformer according to claim 1 wherein said wire is bifilar wound around said former.

3. A transformer according to claim :2 wherein a metal References Cited UNITED STATES PATENTS 1/ 1952 Kolster 343-82l l/1966 Kitamura et al. 34382l X ELI LIEBERMAN, Primary Examiner. 

